Singer is a veteran activist investor who oversees $23 billion and the bid comes amid signs that 2014 could be a year in which activist investors shake up the markets like never before. Shares of spiked by more than 11% in Wednesday trading to $19.93 after the purchase offer was announced, suggesting that some investors think higher bids will come.

“We believe in the quality of Riverbed’s assets,” Jesse Cohn, an Elliott portfolio manager wrote in a letter to Riverbed’s board of directors. “However, Riverbed’s valuation has been impaired by slowing growth in its core WAN optimization market and by significant investments in both acquisitions and operating expenses undertaken to diversify away from the core WAN optimization business.”

Elliott Associates first took a stake in Riverbed in September and by November the New York-based activist hedge fund had disclosed a 10.4% stake in the company, causing the company’s stock to rise. Elliott has said it believes the company is “significantly undervalued.”

Riverbed has certainly not been appreciated by stock investors. In the last two years, its shares have tumbled by 34% and would have been further depressed if not for Elliott’s agitation. The hedge fund has taken a keen interest in network technology companies and played an activist role recently in NetApp and .

In its letter on Wednesday, Elliott said it had communicated its views to Riverbed’s board and met with Riverbed CEO and co-founder Jerry Kennelly, but that the board has “not indicated a desire to explore the significant acquisition interest of numerous potential bidders.” Elliott may be angling to put the company in play for another outfit to buy, but for now it is offering to purchase Riverbed itself.